If your plane is balancing at the rearmost advised CG location without the battery, and of course with an empty fuel tank, I would think you'll be ok if you put the battery as far forward as possible. Get as close as you can to the recommended control throws for the maiden flight, and adjust from there to suit your flying style and preferences. Just make sure the CG isn't behind the rearmost recommended location, else as I'm sure you know, your first flight could be a handful. Good luck and enjoy!